This invention relates to an automatic retrain method for full duplex modems having an echo canceller and an equalizer.
When signal receiving conditions deteriorate during data transmssion between the prior art full duplex modems using an echo canceller (hereinafter referred to simply as modems), it is necessary to automatically retrain the echo canceller and the automatic equalizer within the modems in order to secure accurate data transmission. A retrain procedure for such a case has been proposed as Recommendation V. 32 of the Consultative Committee for International Telegraph and Telephone (CCITT). This retrain procedure, however, is defective in that it requires too much time until the resumption of data transmission because the recommended procedure always requires retraining of both the echo canceller and the automatic equalizer in the modems even if the retrain of the automatic equalizer alone would have been sufficient to permit resumption of data transmission.